Stents are generally cylindrical shaped devices that are radially expandable to hold open a segment of a blood vessel or other anatomical lumen after implantation into the body lumen. Stents have been developed with coatings to deliver drugs or other therapeutic agents.
Stents are used in conjunction with balloon catheters in a variety of medical therapeutic applications including intravascular angioplasty. For example, a balloon catheter device is inflated during PTCA (percutaneous transluminal coronary angioplasty) to dilate a stenotic blood vessel. The stenosis may be the result of a lesion such as a plaque or thrombus. After inflation, the pressurized balloon exerts a compressive force on the lesion thereby increasing the inner diameter of the affected vessel. The increased interior vessel diameter facilitates improved blood flow. Soon after the procedure, however, a significant proportion of treated vessels re-narrow.
To prevent restenosis, short flexible cylinders, or stents, constructed of metal or various polymers are implanted within the vessel to maintain lumen size. The stents acts as a scaffold to support the lumen in an open position. Various configurations of stents include a cylindrical tube defined by a mesh, interconnected stents or like segments. Some exemplary stents are disclosed in U.S. Pat. No. 5,292,331 to Boneau, U.S. Pat. No. 6,090,127 to Globerman, U.S. Pat. No. 5,133,732 to Wiktor, U.S. Pat. No. 4,739,762 to Palmaz and U.S. Pat. No. 5,421,955 to Lau. Balloon-expandable stents are mounted on a collapsed balloon at a diameter smaller than when the stents are deployed.
Stents have been used with coatings to deliver drug or other therapy at the site of the stent, but have certain limitations. Typically, a thin coating is required so that the coating can adhere to the metal or other material forming the stent and so that the stent profile remains small. This limits the amount of drug that can be loaded within the coating. It is also difficult to manufacture and deliver a stent with a uniform coating. This creates uncertainty about the dosage of drug delivered to the patient and increases the cost because additional drug must be loaded to assure an effective dose. Typically, the coating is applied over the whole stent. This results in medication of normal, undamaged tissue at the end of the stent, where treatment may not be necessary or desirable. The uniform coating also delivers the same therapy inside and outside the stent, and over the length of the stent.
Alternative strategies for delivering drugs or other therapies at the site of the stent have included sheaths enclosing all or almost all of the stent. The stent supports the sheath and maintains the sheath against the lumen wall. Problems can arise if the sheath covers side branch arteries, vessels, or other lumens extending from the main lumen in which the stent is installed. The sheath can reduce blood flow to or from the side branch and deliver medication into the side branch where it is unnecessary.
U.S. Pat. No. 6,019,789 to Dinh, et al. discloses use of a stent as a scaffold or structural member for carrying a polymer stent or sheath which preferably contains a therapeutic agent.
U.S. Pat. No. 5,674,242 to Phan et al. discloses an endoprosthetic device for insertion at a vascular site composed of a structural member carrying a polymer member having an embedded therapeutic compound. The polymer member is formed of a shape-memory polymer for expansion upon exposure to a selected stimulus. The polymer member is coextensive with the structural member, or, in other embodiments, the polymer member encases the structural member and, in its contracted state, is effective to restrain the structural member in its contracted state.
U.S. Pat. No. 5,383,928 to Scott et al. discloses a sheath for encompassing at least a portion of a stent to locally deliver a drug to an arterial wall or lumen into which the stent has been inserted, comprising a polymer and a drug incorporated within the polymer, the polymer sheath encompassing at least a portion of the stent and having a thickness to allow controlled release of the drug.
WIPO International Publication No. WO00/12147 to Yang et al. discloses a device adapted for mounting on a stent, the device comprising a sheath being made of polymeric material that includes drugs such as pharmaceutical agent(s) or radioactive agent(s) for delivery to an implant site. The sheath includes a main body of generally tubular shape, and may include mounting means for attaching same to stent. The device may have a slit therein, and may comprise a helical coil, a cylinder or any other suitable shape or design which fits a particular stent. The sheath may include a coating or coatings thereon, containing drugs, surgical adhesives or a combination thereof.
During the procedure, the balloon stent catheter is advanced through a network of tortuous blood vessels. Furthermore, the balloon stent catheter also may encounter narrowed lumens or lumens that are obstructed. Once at the desired site, the balloon is inflated and expands the stent to a final diameter. After deployment, the stent remains in the vessel and the balloon catheter is removed.
The position of the stent on the balloon should be maintained while the balloon stent catheter is moved longitudinally through the network of vessels. In moving to the implant site, the stent may be shifted on the balloon so that the stent may not expand fully along its length or completely dislodged from the balloon. Current strategies for retaining the stent on the balloon include: plastically deforming the stent so that it is crimped onto the balloon; increasing the friction forces between the stent and balloon by modifying the balloon through heat, pressure, or chemical or adhesive means; adding retainers that physically prevent the stent movement; and combinations thereof.
U.S. Pat. No. 4,950,227 to Savin discloses a strategy for stent retention that utilizes end caps mounted on the catheter. The end caps are adapted to temporarily engage the ends of the stent while permitting the stent ends to release when the stent is expanded.
U.S. Pat. Nos. 5,836,965 and 6,159,229 issued Dec. 12, 2000 to Jendersee et al. discloses a strategy for stent retention utilizing a heating process to deform the balloon about the stent while the balloon is heated and preferably pressurized. The balloon expands around and within gaps of the stent causing it to adhere. The balloon continues to adhere as it is cooled and its shape is set. Furthermore, retainers may be placed at the distal and/or proximal ends of the stent.
It would be desirable to have a stent assembly with exterior banding for delivery of therapeutic agents that would overcome the above disadvantages.